1. Field of the Invention
The present invention relates to a zoom lens having an image stabilizing function, and, more particularly, to a zoom lens having an image stabilizing function, which is suited for a television camera, a photographic camera, a video camera or the like, and which has high optical performance over the entire range of variable magnification even during an image stabilizing operation in which a lens unit that is a part of the lens system is made to move in a direction perpendicular to the optical axis so as to correct an image shake caused by the vibration of the zoom lens for the purpose of obtaining a stationary image, with the construction of the zoom lens, such as the refractive power arrangement of the whole zoom lens and the arrangement of the moving lens units for the variation of magnification, appropriately set. Further, the present invention relates to a photographing apparatus having such a zoom lens.
2. Description of Related Art
Heretofore, for use with a television camera, a photographic camera, a video camera or the like, there has been a demand for a zoom lens having high optical performance while having a large relative aperture and a high variable magnification ratio.
In addition to such a demand, in the case of a color television camera for broadcasting, in particular, importance is attached to operability and mobility. In response to such a requirement, the usage of a CCD (charge-coupled device) of ⅔ inch or ½ inch has become the mainstream for an image pickup device in the color television camera.
Since the CCD has an almost uniform resolution over the entire image pickup range, a zoom lens to be associated with the CCD is also required to have an almost uniform resolution from the center of an image plane to the periphery thereof.
For example, the zoom lens is required to have the various aberrations, such as coma, astigmatism and distortion, corrected well and to have high optical performance over the entire image plane. In addition, the zoom lens is required to have a large relative aperture, a wide angle of view and a high variable magnification ratio while being small in size and light in weight, and moreover to have a long back focal distance for enabling a color separation optical system and a variety of filters to be disposed in front of an image pickup means.
In addition, it has become a large problem to suppress an image shake caused by the vibration of a photographing system which has a long focal length or the vibration of hands holding the photographing system. Accordingly, a demand for an image stabilizing function of preventing an image shake has risen. Under the circumstances, there have been proposed a variety of types of image stabilizing methods.
In Japanese Laid-Open Patent Application No. Sho 61-223819, there has been proposed a photographing system in which a refraction-type variable angle prism is disposed on the most object side of the photographing system so as to stabilize an image by varying an apex angle of the refraction-type variable angle prism according to the vibration of the photographing system.
In Japanese Laid-Open Patent Application No. Hei 1-116619, Japanese Laid-Open Patent Application No. Hei 2-124521, etc., there has been proposed a method of obtaining a stationary image by detecting the vibration of a photographing system by means of an acceleration sensor or the like and causing a lens unit that is a part of the photographing system to shift in a direction perpendicular to the optical axis according to a signal obtained by the acceleration sensor or the like.
In Japanese Laid-Open Patent Application No. Hei 7-92431, there has been proposed a zoom lens comprising four lens units, i.e., in order from the object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power, in which the fourth lens unit is composed of a front lens subunit of positive refractive power and a rear lens subunit of positive refractive power, and the shaking of a photographed image caused by the vibration of the zoom lens is corrected by moving the front lens subunit in a direction perpendicular to the optical axis.
In Japanese Laid-Open Patent Application No. Hei 10-90601, there has been proposed a zoom lens comprising five lens units, i.e., in order from the object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, a fourth lens unit of negative refractive power and a fifth lens unit of positive refractive power, in which the shaking of a photographed image caused by the vibration of the zoom lens is corrected by moving the fourth lens unit in a direction perpendicular to the optical axis.
In Japanese Laid-Open Patent Application No. Hei 5-232410, there has been proposed a telephoto-type zoom lens comprising four lens units, i.e., in order from the object side, first to fourth lens units of positive, negative, positive and positive refractive powers, respectively, in which the image stabilization is performed by moving the second lens unit in a direction perpendicular to the optical axis.
In Japanese Laid-Open Patent Application No. Hei 7-152002, there has been proposed a zoom lens comprising four lens units, i.e., in order from the object side, first to fourth lens units of negative, positive, negative and positive refractive powers, respectively, in which the image stabilization is performed by moving the third lens unit in a direction perpendicular to the optical axis.
In Japanese Laid-Open Patent Application No. Hei 7-199124, there has been proposed a variable magnification optical system comprising four lens units, i.e., in order from the object side, first to fourth lens units of positive, negative, positive and positive refractive powers, respectively, in which the image stabilization is performed by moving the whole of the third lens unit in a direction perpendicular to the optical axis.
In general, the method of obtaining a stationary image by disposing an image stabilizing optical system in front of a photographing system and driving and controlling a movable lens unit that is a part of the image stabilizing optical system to prevent the shaking of a photographed image causes such a problem that the whole apparatus becomes large in size and a moving mechanism for moving the movable lens unit becomes complicated.
In an optical system in which the image stabilization is performed by means of a variable angle prism, a problem arises in that the amount of occurrence of decentering lateral chromatic aberration becomes large, in particular, on the telephoto side during the image stabilization.
On the other hand, in an optical system in which the image stabilization is performed by causing a lens unit that is a part of a photographing system to decenter in a direction perpendicular to the optical axis, although there is such an advantage that it is unnecessary to provide a specific optical system used for the image stabilization, a problem arises in that a space is required for the lens unit to be moved and the amount of occurrence of decentering aberration during the image stabilization becomes large.
In the four-unit zoom lens composed of four lens units of positive, negative, positive and positive refractive powers, respectively, in which the image stabilization is performed by moving the front lens subunit of positive refractive power of the fourth lens unit in a direction perpendicular to the optical axis, as proposed in Japanese Laid-Open Patent Application No. Hei 7-92431, the front lens subunit of positive refractive power serving as an image-stabilizing lens unit has a relatively large effective diameter, and, as a result, there is a tendency for the image-stabilizing lens unit to become large and heavy to increase the size of a driving mechanism for the image-stabilizing lens unit.
In the five-unit zoom lens composed of five lens units of positive, negative, positive, negative and positive refractive powers, respectively, in which the image stabilization is performed by moving the fourth lens unit in a direction perpendicular to the optical axis, as proposed in Japanese Laid-Open Patent Application No. Hei 10-90601, since the fourth lens unit is a lens unit arranged to move in the optical axis direction during the variation of magnification, there is a tendency for a driving control mechanism for the fourth lens unit to become complicated.